Summary
DMARC failures for forwarded emails are a persistent challenge, especially when recipients' internal systems, like Microsoft 365 or cloud security appliances, modify email headers or IP addresses during the forwarding process. This often breaks SPF and DKIM authentication, leading to DMARC alignment failures. While the original sender's email may be properly authenticated, the forwarded version often isn't, causing deliverability issues for crucial alerts or internal communications. Addressing this requires understanding the technical nuances of email forwarding and exploring indirect solutions, given that direct control over recipient systems is usually impossible.
Key findings
- Common issue: Forwarded emails frequently fail DMARC checks, particularly those routed through services like Microsoft 365, due to modifications that invalidate SPF and DKIM. SPF is especially vulnerable to forwarding as it relies on the sending IP, which changes during forwarding. You can learn more about how email forwarding affects SPF, DKIM, and DMARC validation.
- Authentication breakdown: Despite originating from properly aligned systems, forwarded messages often show DMARC failures because both SPF and DKIM authentication are broken by the forwarding mechanism.
- Subdomain impact: A subdomain dedicated to alerts might experience higher DMARC failure rates for forwarded mail, even if the primary domain has a strong DMARC pass rate and a reject policy.
- Limited visibility: DMARC reports may indicate failures but often lack granular detail on whether the email was rejected, quarantined, or delivered, making troubleshooting challenging.
- Beyond O365: While Microsoft 365 is a common culprit, other services and cloud-based security appliances, including those on AWS ranges, can also contribute to DMARC failures through improper forwarding.
Key considerations
- No direct control: Senders typically cannot dictate how recipients' email systems handle forwarding, limiting direct technical solutions.
- Policy implications: A DMARC policy of p=reject can lead to legitimate forwarded emails being blocked, causing critical alerts to be missed. Understanding how email forwarding and DMARC policies affect delivery is crucial.
- Recipient outreach: If feasible, educating recipients about adding the sender to their allow-list can mitigate some issues, but this is often impractical for a large, unknown audience.
- Alternative channels: For critical alerts, consider offering alternative notification methods beyond email, such as webhooks, SMS, or direct integrations (e.g., PagerDuty, Signal), to ensure delivery.
- DMARC report analysis: Utilize DMARC reports to identify the sources of failures, even if detailed disposition is missing. Aggregating and analyzing reports can reveal problematic domains or IP ranges. More on why DMARC fails for forwarded emails.
What email marketers say
Email marketers often face the difficult reality of DMARC failures stemming from recipient-side forwarding, especially with automated system alerts that are critical but not directly revenue-generating. The consensus among marketers is that while the problem is widespread, particularly with Microsoft 365, direct intervention is often impossible. This forces a focus on mitigation strategies, such as recipient education, exploring alternative communication channels, or adjusting DMARC policies to avoid blocking essential messages.
Key opinions
- M365 prevalence: Many marketers observe that Microsoft 365 accounts are frequent sources of DMARC failures due to incorrectly configured forwarding rules.
- Limited control: It is generally acknowledged that senders cannot control or modify how recipients' email systems (including M365) handle email forwarding.
- Reporting challenges: Analyzing DMARC reports manually to identify specific failing recipients or the exact disposition of messages can be extremely difficult. This highlights the importance of tools that diagnose DMARC failures using DMARC reports.
- Allow-listing outreach: Targeted or broadcast outreach to encourage recipients to add the sender to an allow-list is considered a viable, albeit challenging, social solution.
- Alert functionality: When emails are used for critical alerts, the risk of DMARC failures means these alerts may not reach their intended recipients, impacting system monitoring or operational efficiency.
Key considerations
- Policy adjustment: Given uncontrollable forwarding behavior, some marketers may opt for a less stringent DMARC policy, such as p=quarantine instead of p=reject, to avoid blocking important forwarded messages.
- Identify problem domains: Even without direct control, analyzing DMARC reports can help identify specific recipient domains or IP ranges that consistently cause failures, allowing for more targeted communication if possible.
- Non-marketing context: It is important to remember that DMARC failures due to forwarding can affect transactional or alert emails, not just marketing messages, complicating the resolution approach.
- Alternative notification systems: For critical information, integrating non-email based alert systems can provide a reliable fallback when email forwarding is problematic.
- Rogue reports: Consider the possibility that some DMARC failure reports might be generated by recipient-side appliances that ignore authentication errors, yet still send reports, leading to misleading data. This is a common reason DMARC fails.
Marketer view
Marketer from Email Geeks states that Microsoft 365 accounts are a common source of DMARC failures, often due to improper forwarding configurations. They suggest that if mail flow cannot be changed, a targeted outreach to recipients, asking them to allow-list the sender, is likely the best course of action. They also propose considering a secondary channel, such as PagerDuty or Signal, as an alert endpoint to mitigate the problem.
Marketer view
Marketer from Email Geeks points out that it's challenging to identify which specific recipients are causing DMARC failures or even determine if the mail is being rejected, as their DMARC reporting service doesn't provide disposition data. They indicate that manually sifting through DMARC reports to pinpoint failures is difficult without advanced SQL query skills.
What the experts say
Email experts understand that DMARC failures for forwarded mail are an inherent challenge due to how email authentication protocols interact with mail transfer agents (MTAs) that modify messages. While direct control over recipient forwarding is rare, experts focus on sender-side best practices, such as robust DKIM signing and the strategic use of DMARC policies. They also emphasize the emerging role of ARC (Authenticated Received Chain) as a potential long-term solution, although its widespread adoption by forwarding services is still evolving.
Key opinions
- Authentication decay: Experts confirm that traditional forwarding mechanisms often break SPF and can invalidate DKIM signatures if headers are altered, leading to DMARC failure. This issue is a fundamental aspect of email authentication.
- ARC's role: Authenticated Received Chain (ARC) is designed to preserve authentication results across forwarding hops. While not universally adopted, it is seen as the primary technical solution to DMARC failures with forwarded mail. Learn more about how to implement ARC.
- DKIM importance: Strong and persistent DKIM signing is crucial, as it is more resilient to forwarding than SPF. Ensuring a valid DKIM signature that survives forwarding can help maintain DMARC alignment.
- Policy choice: Experts often advise caution with a p=reject policy in scenarios with significant legitimate forwarding, suggesting p=quarantine or p=none while investigating. Consider how to roll out DMARC enforcement carefully.
Key considerations
- Sender responsibility: Even with forwarding challenges, senders are responsible for ensuring their initial authentication is impeccable, providing the best possible foundation for deliverability.
- DMARC monitoring: Continuous monitoring of DMARC reports is vital for identifying patterns of failure and understanding which forwarding networks are most problematic. For more, see email forwarding impacts on DMARC.
- Policy adjustment: For sensitive or critical communications, a DMARC policy that allows for greater tolerance of forwarding, like p=none, might be necessary to ensure delivery, even if it compromises strict enforcement against spoofing.
- Education and advocacy: While challenging, advocating for recipient-side adoption of ARC or proper forwarding configurations remains a long-term goal for the industry.
Expert view
Expert from SpamResource explains that SPF fails when emails are forwarded because the SPF check is performed against the IP address of the last hop, which becomes the forwarding server's IP rather than the original sender's. This often leads to authentication failure if the forwarding server's IP is not authorized in the sender's SPF record.
Expert view
Expert from Word to the Wise suggests that while DKIM is generally more resilient to forwarding than SPF, changes to the email's body or headers during forwarding can still break the DKIM signature. They advise senders to ensure their DKIM implementation is robust to withstand minor modifications.
What the documentation says
Official documentation and technical guides consistently highlight that email forwarding, by its very nature, can interfere with DMARC authentication mechanisms like SPF and DKIM. While DMARC is critical for security, its strict alignment requirements are often at odds with how email forwarding services operate. The Authenticated Received Chain (ARC) is introduced as the standard protocol to mitigate this, providing a chain of custody for email authentication results across multiple hops. Understanding these technical underpinnings is vital for troubleshooting and managing DMARC policies effectively.
Key findings
- SPF invalidation: Documentation confirms that when an email is forwarded, the IP address changes, causing SPF authentication to fail because the new sending IP is not authorized in the original sender's SPF record.
- DKIM fragility: While DKIM is more robust, forwarding services can sometimes modify email headers or body content, breaking the DKIM signature and leading to DMARC failure.
- DMARC alignment: DMARC requires either SPF or DKIM to pass AND align with the From domain. Forwarding disrupts this alignment, leading to DMARC failures.
- ARC as a solution: Authenticated Received Chain (ARC) is a protocol designed to preserve original email authentication results (SPF, DKIM, DMARC) across forwarding hops, allowing receiving mail servers to validate the legitimacy of forwarded messages. This is part of an advanced guide to email authentication.
Key considerations
- DKIM signing: Documentation often emphasizes the importance of DKIM signing all outgoing emails with the sender's domain, as DKIM is more resilient to changes introduced by forwarding than SPF.
- Policy enforcement: DMARC policies (p=none, p=quarantine, p=reject) must be carefully chosen, considering the impact on legitimate forwarded emails. A more lenient policy might be necessary if critical forwarded mail is affected. For examples, see simple DMARC policy examples.
- DMARC reporting: Regularly reviewing DMARC reports (aggregate and forensic) is essential to identify the scale and source of forwarding-related failures and to refine policies. Common pitfalls in DMARC configuration often include ignoring these reports.
- PostSRSd: Some technical documentation mentions solutions like PostSRSd for re-signing DKIM headers for forwarded mail, but this requires control over the forwarding mail server, which is typically not held by the original sender.
Technical article
Documentation from DuoCircle outlines that a common reason for DMARC failures is domain alignment issues, where DMARC verifies if the domain in the From header aligns with the SPF and DKIM authentication results. Forwarding often disrupts this alignment, leading to authentication failures.
Technical article
Documentation from GoDMARC Knowledge Base explains that email forwarding affects DMARC authentication by potentially altering email content or headers, which can break SPF and DKIM. They discuss potential challenges this creates and offer best practices to mitigate issues while maintaining security protocols.
Related resources
15 resources
Related pages
How does email forwarding affect SPF, DKIM, and DMARC validation?
How to troubleshoot DMARC failures and their impact on email deliverability?
How to implement ARC (Authenticated Received Chain) and how does it affect DMARC failures from forwarding?
Simple DMARC examples: how to start with a p=none policy
How to safely transition your DMARC policy to quarantine or reject
Understanding and troubleshooting DMARC reports from Google and Yahoo
An advanced guide to email authentication - beyond the basics
Why Your Emails Fail: Expert Guide to Improve Email Deliverability [2025]
How do email forwarding and DMARC policies affect email delivery and reporting?
Why does DMARC authentication fail when SPF and DKIM pass, and how can it be fixed?
